Question 7
When gold-bearing ore is finely ground and mixed into a flowing stream of water, why does the gold travel to the bottom first?
The right answer is the one marked above.
Because the density of gold is very high. It settles ahead of the impurities, and that is what separates it out.
Gold does not dissolve in water, nor does it react with it — its reactivity is very low. Were it lighter it would float, which is the exact opposite.